Mermaid Image Generator

Generate PNG/SVG images from Mermaid diagram syntax using mermaid.ink API. Zero dependencies - uses only Node.js built-in modules and curl. Use when users ne...

Convert Mermaid diagram syntax to PNG/SVG images using the mermaid.ink online rendering API. Zero dependencies - uses only Node.js built-in modules and curl.

Quick Start

# From a .mmd file
node scripts/mermaid-to-image.js diagram.mmd output.png

# From stdin
echo "flowchart LR; A --> B" | node scripts/mermaid-to-image.js - output.png

# Generate SVG instead
node scripts/mermaid-to-image.js diagram.mmd output.svg

When to Use This Skill

Use this skill when:

• User asks to "draw a diagram", "create a flowchart", "make a visual"
• User needs diagram images for PPTs, documentation, or presentations
• User wants to convert Mermaid code to shareable image files
• Local Mermaid CLI (mmdc) is unavailable or has dependency issues

Script Usage

Basic Conversion

node scripts/mermaid-to-image.js <input> <output>

Input options:

• File path: diagram.mmd
• Stdin: - (pipe Mermaid code directly)

Output format: Determined by file extension (.png or .svg)

Examples

Example 1: Convert file to PNG

node scripts/mermaid-to-image.js flowchart.mmd flowchart.png

Example 2: Pipe from stdin

cat <<EOF | node scripts/mermaid-to-image.js - sequence.png
sequenceDiagram
    Alice->>Bob: Hello
    Bob-->>Alice: Hi
EOF

Example 3: Generate SVG for web

node scripts/mermaid-to-image.js architecture.mmd architecture.svg

Mermaid Diagram Types

This skill supports all Mermaid diagram types:

Type	Use Case
flowchart	Processes, algorithms, user journeys
sequenceDiagram	API flows, interactions over time
classDiagram	OOP design, domain models
erDiagram	Database schemas
stateDiagram	State machines
gantt	Project timelines
pie	Proportional data
gitGraph	Git branching strategies

Example Mermaid Code

Flowchart

flowchart LR
    A[Start] --> B{Decision}
    B -->|Yes| C[Action 1]
    B -->|No| D[Action 2]
    C --> E[End]
    D --> E

Sequence Diagram

sequenceDiagram
    participant User
    participant API
    participant Database
    
    User->>API: POST /login
    API->>Database: Query
    Database-->>API: Result
    API-->>User: Response

Class Diagram

classDiagram
    Animal <|-- Duck
    Animal <|-- Fish
    Animal: +int age
    Animal: +String gender
    Animal: +isMammal()

API Details

Service: mermaid.ink Endpoints:

• PNG: https://mermaid.ink/img/{base64_code}
• SVG: https://mermaid.ink/svg/{base64_code}

Advantages:

• ✅ No local dependencies (no Chrome/Puppeteer needed)
• ✅ Free and fast
• ✅ Returns high-quality PNG/SVG
• ✅ Works in headless environments

Limitations:

• Requires internet connection
• Diagram code is sent to external service (don't use for sensitive data)

Error Handling

The script handles common errors:

❌ File not found: diagram.mmd
❌ API request failed: 400 Bad Request
❌ Failed to connect to mermaid.ink: Connection timeout

Troubleshooting:

1. Check internet connectivity
2. Verify Mermaid syntax at https://mermaid.live
3. Ensure output directory exists (script creates it automatically)

Integration Pattern

When creating diagrams for users:

1. Write Mermaid code → Save to .mmd file or use stdin
2. Run conversion script → Generate PNG/SVG
3. Send/deliver image → Attach to response or save to specified location

Example workflow:

# 1. Create diagram
cat > openclaw-flow.mmd <<EOF
flowchart LR
    User --> OpenClaw
    OpenClaw --> Tools
EOF

# 2. Convert to image
node scripts/mermaid-to-image.js openclaw-flow.mmd openclaw-flow.png

# 3. Use the image (send via message, save, etc.)

Best Practices

1. Keep diagrams simple - Under 15 nodes for readability
2. Use meaningful labels - Self-documenting diagrams
3. Test syntax first - Validate at mermaid.live before converting
4. Choose format wisely - PNG for PPTs, SVG for web/docs
5. Add comments - Use %% for in-diagram documentation

Security Notes

• Diagram code is sent to mermaid.ink API
• Do not include sensitive information in diagrams
• For sensitive data, use local Mermaid CLI instead